I was at the NYSE opening bell ringing today for the first day of trading of PIMCO Total Return ETF (NYSEArca: TRXT), a huge event for the exchange traded fund business.

The launch was very successful with over a half-million shares traded already today, and likely to hit 1 million by the close. Bid/ask spreads are tight at around a penny. A great showing for the first day. Since the shares are trading around $100, these are significant inflows for a launch.

“Overall, ETFs have become an important part of the PIMCO toolkit,” Total Return ETF manager Bill Gross said. He said the value of the ETF vehicle drove the money manager to enter the business. [PIMCO ETF Puts Focus on Active ETFs]

PIMCO already has an established stable of ETFs including PIMCO Enhanced Short Maturity Strategy Fund (NYSEArca: MINT), but today’s listing is the most important fund launch in recent memory. Everyone will be watching the trading volume and spreads in PIMCO Total Return ETF to judge its liquidity. Advisors could make the switch to the ETF version, which also makes it easier for more individual investors to access the strategy.

The launch “signals an important new phase in the development of the ETF marketplace,” Gross said Thursday. [PIMCO’s Gross: Play Defense]

While I was at the NYSE for open, Bill Gross was at PIMCO’s headquarters in Newport Beach for a simultaneous bell ringing. The manager of the world’s largest mutual fund and the new PIMCO ETF said he rang a bell that’s been at the firm for 30 years.

“When we got a client, we rang the bell,” Gross said in a CNBC interview Thursday, speaking of the firm’s early days in the 1970s. The small group of people then at the company rang the bell and had a “celebratory” drink — of coffee or Coke, the bond manager said — before going about their business for the next one.

But those were the old days. At the end of 2011, PIMCO had over 2,000 employees and more than $1.3 trillion in assets under management.

If PIMCO Total Return ETF follows up on today’s successful launch and attracts large inflows, then we could see other active fund shops follow it into ETFs. Gross has made no secret of the fact he wants the ETF to be the largest in the industry in a couple years. We’ll see.

At the NYSE for the opening bell on PIMCO Total Return ETF’s first day of trading.